﻿/* Copyright Joyent, Inc. and other Node contributors. All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include <assert.h>
#include <stdlib.h>

#include "uv.h"
#include "internal.h"
#include "handle-inl.h"
#include "stream-inl.h"
#include "req-inl.h"


 /*
  * Threshold of active tcp streams for which to preallocate tcp read buffers.
  * (Due to node slab allocator performing poorly under this pattern,
  *  the optimization is temporarily disabled (threshold=0).  This will be
  *  revisited once node allocator is improved.)
  */
const unsigned int uv_active_tcp_streams_threshold = 0;

/*
 * Number of simultaneous pending AcceptEx calls.
 */
const unsigned int uv_simultaneous_server_accepts = 32;

/* A zero-size buffer for use by uv_tcp_read */
static char uv_zero_[] = "";

static int uv__tcp_nodelay(uv_tcp_t* handle, SOCKET socket, int enable) {
    if (setsockopt(socket,
                   IPPROTO_TCP,
                   TCP_NODELAY,
                   (const char*)&enable,
                   sizeof enable) == -1) {
        return WSAGetLastError();
    }
    return 0;
}

static int set_options(SOCKET socket) {
    do {
#if (defined(WIN32) || defined(_WIN64))
        u_long nonblocking = 1;
        if (socket == INVALID_SOCKET) {
            return 0;
        }
        if (SOCKET_ERROR == ioctlsocket(socket, FIONBIO, &nonblocking)) {
            //verify(0);
            return 0;
        }
#else
        int flags = 0;
        if (socket_fd < 0) {
            verify(0);
            return 1;
        }
        flags = fcntl(socket, F_GETFL, 0);
        fcntl(socket, F_SETFL, flags | O_NONBLOCK);
#endif /* defined(WIN32) || defined(_WIN64) */

    } while (0);
    int nodelay = 1;
    setsockopt(socket, IPPROTO_TCP, TCP_NODELAY, (char*)&nodelay, sizeof(nodelay));
    struct linger linger;
    memset(&linger, 0, sizeof(linger));
    setsockopt(socket, SOL_SOCKET, SO_LINGER, (char*)&linger, sizeof(linger));
    int keepalive = 0;
    setsockopt(socket, SOL_SOCKET, SO_KEEPALIVE, (char*)&keepalive, sizeof(keepalive));
    int r_buf = uv_get_recv_buff_size();
    if (r_buf > 0) {
        setsockopt(socket, SOL_SOCKET, SO_RCVBUF, (const char*)&r_buf, sizeof(int));
    }
    int s_buf = uv_get_send_buff_size();
    if (s_buf > 0) {
        setsockopt(socket, SOL_SOCKET, SO_SNDBUF, (const char*)&s_buf, sizeof(int));
    }
    return 0;
}

static int uv__tcp_keepalive(uv_tcp_t* handle, SOCKET socket, int enable, unsigned int delay) {
    if (setsockopt(socket,
                   SOL_SOCKET,
                   SO_KEEPALIVE,
                   (const char*)&enable,
                   sizeof enable) == -1) {
        return WSAGetLastError();
    }

    if (enable && setsockopt(socket,
                             IPPROTO_TCP,
                             TCP_KEEPALIVE,
                             (const char*)&delay,
                             sizeof delay) == -1) {
        return WSAGetLastError();
    }

    return 0;
}


static int uv_tcp_set_socket(uv_loop_t* loop,
                             uv_tcp_t* handle,
                             SOCKET socket,
                             int family,
                             int imported) {
    DWORD yes = 1;
    int non_ifs_lsp;
    int err;

    if (handle->socket != INVALID_SOCKET)
        return UV_EBUSY;

    /* Set the socket to nonblocking mode */
    if (ioctlsocket(socket, FIONBIO, &yes) == SOCKET_ERROR) {
        return WSAGetLastError();
    }

    /* Make the socket non-inheritable */
    if (!SetHandleInformation((HANDLE)socket, HANDLE_FLAG_INHERIT, 0))
        return GetLastError();

    /* Associate it with the I/O completion port. Use uv_handle_t pointer as
     * completion key. */
    if (CreateIoCompletionPort((HANDLE)socket,
                               loop->iocp,
                               (ULONG_PTR)socket,
                               0) == NULL) {
        if (imported) {
            handle->flags |= UV_HANDLE_EMULATE_IOCP;
        } else {
            return GetLastError();
        }
    }

    if (family == AF_INET6) {
        non_ifs_lsp = uv_tcp_non_ifs_lsp_ipv6;
    } else {
        non_ifs_lsp = uv_tcp_non_ifs_lsp_ipv4;
    }

    if (!(handle->flags & UV_HANDLE_EMULATE_IOCP) && !non_ifs_lsp) {
        UCHAR sfcnm_flags =
            FILE_SKIP_SET_EVENT_ON_HANDLE | FILE_SKIP_COMPLETION_PORT_ON_SUCCESS;
        if (!SetFileCompletionNotificationModes((HANDLE)socket, sfcnm_flags))
            return GetLastError();
        handle->flags |= UV_HANDLE_SYNC_BYPASS_IOCP;
    }

    if (handle->flags & UV_HANDLE_TCP_NODELAY) {
        err = uv__tcp_nodelay(handle, socket, 1);
        if (err)
            return err;
    }

    /* TODO: Use stored delay. */
    if (handle->flags & UV_HANDLE_TCP_KEEPALIVE) {
        err = uv__tcp_keepalive(handle, socket, 1, 60);
        if (err)
            return err;
    }
    set_options(socket);
    handle->socket = socket;

    if (family == AF_INET6) {
        handle->flags |= UV_HANDLE_IPV6;
    } else {
        assert(!(handle->flags & UV_HANDLE_IPV6));
    }

    return 0;
}


int uv_tcp_init_ex(uv_loop_t* loop, uv_tcp_t* handle, unsigned int flags) {
    int domain;

    /* Use the lower 8 bits for the domain */
    domain = flags & 0xFF;
    if (domain != AF_INET && domain != AF_INET6 && domain != AF_UNSPEC)
        return UV_EINVAL;

    if (flags & ~0xFF)
        return UV_EINVAL;

    uv_stream_init(loop, (uv_stream_t*)handle, UV_TCP);
    handle->tcp.serv.accept_reqs = NULL;
    handle->tcp.serv.pending_accepts = NULL;
    handle->socket = INVALID_SOCKET;
    handle->reqs_pending = 0;
    handle->tcp.serv.func_acceptex = NULL;
    handle->tcp.conn.func_connectex = NULL;
    handle->tcp.serv.processed_accepts = 0;
    handle->delayed_error = 0;

    /* If anything fails beyond this point we need to remove the handle from
     * the handle queue, since it was added by uv__handle_init in uv_stream_init.
     */

    if (domain != AF_UNSPEC) {
        SOCKET sock;
        DWORD err;

        sock = socket(domain, SOCK_STREAM, 0);
        if (sock == INVALID_SOCKET) {
            err = WSAGetLastError();
            QUEUE_REMOVE(&handle->handle_queue);
            return uv_translate_sys_error(err);
        }

        err = uv_tcp_set_socket(handle->loop, handle, sock, domain, 0);
        if (err) {
            closesocket(sock);
            QUEUE_REMOVE(&handle->handle_queue);
            return uv_translate_sys_error(err);
        }

    }

    return 0;
}


int uv_tcp_init(uv_loop_t* loop, uv_tcp_t* handle) {
    return uv_tcp_init_ex(loop, handle, AF_UNSPEC);
}


void uv_tcp_endgame(uv_loop_t* loop, uv_tcp_t* handle) {
    int err;
    unsigned int i;
    uv_tcp_accept_t* req;

    if (handle->flags & UV_HANDLE_CONNECTION &&
        handle->stream.conn.shutdown_req != NULL &&
        handle->stream.conn.write_reqs_pending == 0) {

        UNREGISTER_HANDLE_REQ(loop, handle, handle->stream.conn.shutdown_req);

        err = 0;
        if (handle->flags & UV_HANDLE_CLOSING) {
            err = ERROR_OPERATION_ABORTED;
        } else if (shutdown(handle->socket, SD_SEND) == SOCKET_ERROR) {
            err = WSAGetLastError();
        }

        if (handle->stream.conn.shutdown_req->cb) {
            handle->stream.conn.shutdown_req->cb(handle->stream.conn.shutdown_req,
                                                 uv_translate_sys_error(err));
        }

        handle->stream.conn.shutdown_req = NULL;
        DECREASE_PENDING_REQ_COUNT(handle);
        return;
    }

    if (handle->flags & UV_HANDLE_CLOSING &&
        handle->reqs_pending == 0) {
        assert(!(handle->flags & UV_HANDLE_CLOSED));
        assert(handle->socket == INVALID_SOCKET);

        if (!(handle->flags & UV_HANDLE_CONNECTION) && handle->tcp.serv.accept_reqs) {
            if (handle->flags & UV_HANDLE_EMULATE_IOCP) {
                for (i = 0; i < uv_simultaneous_server_accepts; i++) {
                    req = &handle->tcp.serv.accept_reqs[i];
                    if (req->wait_handle != INVALID_HANDLE_VALUE) {
                        UnregisterWait(req->wait_handle);
                        req->wait_handle = INVALID_HANDLE_VALUE;
                    }
                    if (req->event_handle != NULL) {
                        CloseHandle(req->event_handle);
                        req->event_handle = NULL;
                    }
                }
            }

            uv__free(handle->tcp.serv.accept_reqs);
            handle->tcp.serv.accept_reqs = NULL;
        }

        if (handle->flags & UV_HANDLE_CONNECTION &&
            handle->flags & UV_HANDLE_EMULATE_IOCP) {
            if (handle->read_req.wait_handle != INVALID_HANDLE_VALUE) {
                UnregisterWait(handle->read_req.wait_handle);
                handle->read_req.wait_handle = INVALID_HANDLE_VALUE;
            }
            if (handle->read_req.event_handle != NULL) {
                CloseHandle(handle->read_req.event_handle);
                handle->read_req.event_handle = NULL;
            }
        }

        uv__handle_close(handle);
        loop->active_tcp_streams--;
    }
}


/* Unlike on Unix, here we don't set SO_REUSEADDR, because it doesn't just
 * allow binding to addresses that are in use by sockets in TIME_WAIT, it
 * effectively allows 'stealing' a port which is in use by another application.
 *
 * SO_EXCLUSIVEADDRUSE is also not good here because it does check all sockets,
 * regardless of state, so we'd get an error even if the port is in use by a
 * socket in TIME_WAIT state.
 *
 * See issue #1360.
 *
 */
static int uv_tcp_try_bind(uv_tcp_t* handle,
                           const struct sockaddr* addr,
                           unsigned int addrlen,
                           unsigned int flags) {
    DWORD err;
    int r;

    if (handle->socket == INVALID_SOCKET) {
        SOCKET sock;

        /* Cannot set IPv6-only mode on non-IPv6 socket. */
        if ((flags & UV_TCP_IPV6ONLY) && addr->sa_family != AF_INET6)
            return ERROR_INVALID_PARAMETER;

        sock = socket(addr->sa_family, SOCK_STREAM, 0);
        if (sock == INVALID_SOCKET) {
            return WSAGetLastError();
        }

        err = uv_tcp_set_socket(handle->loop, handle, sock, addr->sa_family, 0);
        if (err) {
            closesocket(sock);
            return err;
        }
    }

#ifdef IPV6_V6ONLY
    if (addr->sa_family == AF_INET6) {
        int on;

        on = (flags & UV_TCP_IPV6ONLY) != 0;

        /* TODO: how to handle errors? This may fail if there is no ipv4 stack
         * available, or when run on XP/2003 which have no support for dualstack
         * sockets. For now we're silently ignoring the error. */
        setsockopt(handle->socket,
                   IPPROTO_IPV6,
                   IPV6_V6ONLY,
                   (const char*)&on,
                   sizeof on);
    }
#endif

    r = bind(handle->socket, addr, addrlen);

    if (r == SOCKET_ERROR) {
        err = WSAGetLastError();
        if (err == WSAEADDRINUSE) {
            /* Some errors are not to be reported until connect() or listen() */
            handle->delayed_error = err;
        } else {
            return err;
        }
    }

    handle->flags |= UV_HANDLE_BOUND;

    return 0;
}


static void CALLBACK post_completion(void* context, BOOLEAN timed_out) {
    uv_req_t* req;
    uv_tcp_t* handle;

    req = (uv_req_t*)context;
    assert(req != NULL);
    handle = (uv_tcp_t*)req->data;
    assert(handle != NULL);
    assert(!timed_out);

    if (!PostQueuedCompletionStatus(handle->loop->iocp,
                                    req->u.io.overlapped.InternalHigh,
                                    0,
                                    &req->u.io.overlapped)) {
        uv_fatal_error(GetLastError(), "PostQueuedCompletionStatus");
    }
}


static void CALLBACK post_write_completion(void* context, BOOLEAN timed_out) {
    uv_write_t* req;
    uv_tcp_t* handle;

    req = (uv_write_t*)context;
    assert(req != NULL);
    handle = (uv_tcp_t*)req->handle;
    assert(handle != NULL);
    assert(!timed_out);

    if (!PostQueuedCompletionStatus(handle->loop->iocp,
                                    req->u.io.overlapped.InternalHigh,
                                    0,
                                    &req->u.io.overlapped)) {
        uv_fatal_error(GetLastError(), "PostQueuedCompletionStatus");
    }
}


static void uv_tcp_queue_accept(uv_tcp_t* handle, uv_tcp_accept_t* req) {
    uv_loop_t* loop = handle->loop;
    BOOL success;
    DWORD bytes;
    SOCKET accept_socket;
    short family;

    assert(handle->flags & UV_HANDLE_LISTENING);
    assert(req->accept_socket == INVALID_SOCKET);

    /* choose family and extension function */
    if (handle->flags & UV_HANDLE_IPV6) {
        family = AF_INET6;
    } else {
        family = AF_INET;
    }

    /* Open a socket for the accepted connection. */
    accept_socket = socket(family, SOCK_STREAM, 0);
    if (accept_socket == INVALID_SOCKET) {
        SET_REQ_ERROR(req, WSAGetLastError());
        uv_insert_pending_req(loop, (uv_req_t*)req);
        handle->reqs_pending++;
        return;
    }

    /* Make the socket non-inheritable */
    if (!SetHandleInformation((HANDLE)accept_socket, HANDLE_FLAG_INHERIT, 0)) {
        SET_REQ_ERROR(req, GetLastError());
        uv_insert_pending_req(loop, (uv_req_t*)req);
        handle->reqs_pending++;
        closesocket(accept_socket);
        return;
    }

    /* Prepare the overlapped structure. */
    memset(&(req->u.io.overlapped), 0, sizeof(req->u.io.overlapped));
    if (handle->flags & UV_HANDLE_EMULATE_IOCP) {
        assert(req->event_handle != NULL);
        req->u.io.overlapped.hEvent = (HANDLE)((ULONG_PTR)req->event_handle | 1);
    }

    success = handle->tcp.serv.func_acceptex(handle->socket,
                                             accept_socket,
                                             (void*)req->accept_buffer,
                                             0,
                                             sizeof(struct sockaddr_storage),
                                             sizeof(struct sockaddr_storage),
                                             &bytes,
                                             &req->u.io.overlapped);

    if (UV_SUCCEEDED_WITHOUT_IOCP(success)) {
        /* Process the req without IOCP. */
        req->accept_socket = accept_socket;
        handle->reqs_pending++;
        uv_insert_pending_req(loop, (uv_req_t*)req);
    } else if (UV_SUCCEEDED_WITH_IOCP(success)) {
        /* The req will be processed with IOCP. */
        req->accept_socket = accept_socket;
        handle->reqs_pending++;
        if (handle->flags & UV_HANDLE_EMULATE_IOCP &&
            req->wait_handle == INVALID_HANDLE_VALUE &&
            !RegisterWaitForSingleObject(&req->wait_handle,
                                         req->event_handle, post_completion, (void*)req,
                                         INFINITE, WT_EXECUTEINWAITTHREAD)) {
            SET_REQ_ERROR(req, GetLastError());
            uv_insert_pending_req(loop, (uv_req_t*)req);
        }
    } else {
        /* Make this req pending reporting an error. */
        SET_REQ_ERROR(req, WSAGetLastError());
        uv_insert_pending_req(loop, (uv_req_t*)req);
        handle->reqs_pending++;
        /* Destroy the preallocated client socket. */
        closesocket(accept_socket);
        /* Destroy the event handle */
        if (handle->flags & UV_HANDLE_EMULATE_IOCP) {
            CloseHandle(req->event_handle);
            req->event_handle = NULL;
        }
    }
}


static void uv_tcp_queue_read(uv_loop_t* loop, uv_tcp_t* handle) {
    uv_read_t* req;
    uv_buf_t buf;
    int result;
    DWORD bytes, flags;

    assert(handle->flags & UV_HANDLE_READING);
    assert(!(handle->flags & UV_HANDLE_READ_PENDING));

    req = &handle->read_req;
    memset(&req->u.io.overlapped, 0, sizeof(req->u.io.overlapped));

    /*
     * Preallocate a read buffer if the number of active streams is below
     * the threshold.
    */
    if (loop->active_tcp_streams < uv_active_tcp_streams_threshold) {
        handle->flags &= ~UV_HANDLE_ZERO_READ;
        handle->tcp.conn.read_buffer = uv_buf_init(NULL, 0);
        handle->alloc_cb((uv_handle_t*)handle, 65536, &handle->tcp.conn.read_buffer);
        if (handle->tcp.conn.read_buffer.base == NULL ||
            handle->tcp.conn.read_buffer.len == 0) {
            handle->read_cb((uv_stream_t*)handle, UV_ENOBUFS, &handle->tcp.conn.read_buffer);
            return;
        }
        assert(handle->tcp.conn.read_buffer.base != NULL);
        buf = handle->tcp.conn.read_buffer;
    } else {
        handle->flags |= UV_HANDLE_ZERO_READ;
        buf.base = (char*)&uv_zero_;
        buf.len = 0;
    }

    /* Prepare the overlapped structure. */
    memset(&(req->u.io.overlapped), 0, sizeof(req->u.io.overlapped));
    if (handle->flags & UV_HANDLE_EMULATE_IOCP) {
        assert(req->event_handle != NULL);
        req->u.io.overlapped.hEvent = (HANDLE)((ULONG_PTR)req->event_handle | 1);
    }

    flags = 0;
    result = WSARecv(handle->socket,
                     (WSABUF*)&buf,
                     1,
                     &bytes,
                     &flags,
                     &req->u.io.overlapped,
                     NULL);

    handle->flags |= UV_HANDLE_READ_PENDING;
    handle->reqs_pending++;

    if (UV_SUCCEEDED_WITHOUT_IOCP(result == 0)) {
        /* Process the req without IOCP. */
        req->u.io.overlapped.InternalHigh = bytes;
        uv_insert_pending_req(loop, (uv_req_t*)req);
    } else if (UV_SUCCEEDED_WITH_IOCP(result == 0)) {
        /* The req will be processed with IOCP. */
        if (handle->flags & UV_HANDLE_EMULATE_IOCP &&
            req->wait_handle == INVALID_HANDLE_VALUE &&
            !RegisterWaitForSingleObject(&req->wait_handle,
                                         req->event_handle, post_completion, (void*)req,
                                         INFINITE, WT_EXECUTEINWAITTHREAD)) {
            SET_REQ_ERROR(req, GetLastError());
            uv_insert_pending_req(loop, (uv_req_t*)req);
        }
    } else {
        /* Make this req pending reporting an error. */
        SET_REQ_ERROR(req, WSAGetLastError());
        uv_insert_pending_req(loop, (uv_req_t*)req);
    }
}


int uv_tcp_close_reset(uv_tcp_t* handle, uv_close_cb close_cb) {
    struct linger l = {1, 0};

    /* Disallow setting SO_LINGER to zero due to some platform inconsistencies */
    if (handle->flags & UV_HANDLE_SHUTTING)
        return UV_EINVAL;

    if (0 != setsockopt(handle->socket, SOL_SOCKET, SO_LINGER, (const char*)&l, sizeof(l)))
        return uv_translate_sys_error(WSAGetLastError());

    uv_close((uv_handle_t*)handle, close_cb);
    return 0;
}


int uv_tcp_listen(uv_tcp_t* handle, int backlog, uv_connection_cb cb) {
    unsigned int i, simultaneous_accepts;
    uv_tcp_accept_t* req;
    int err;

    assert(backlog > 0);

    if (handle->flags & UV_HANDLE_LISTENING) {
        handle->stream.serv.connection_cb = cb;
    }

    if (handle->flags & UV_HANDLE_READING) {
        return WSAEISCONN;
    }

    if (handle->delayed_error) {
        return handle->delayed_error;
    }

    if (!(handle->flags & UV_HANDLE_BOUND)) {
        err = uv_tcp_try_bind(handle,
                              (const struct sockaddr*)&uv_addr_ip4_any_,
                              sizeof(uv_addr_ip4_any_),
                              0);
        if (err)
            return err;
        if (handle->delayed_error)
            return handle->delayed_error;
    }

    if (!handle->tcp.serv.func_acceptex) {
        if (!uv_get_acceptex_function(handle->socket, &handle->tcp.serv.func_acceptex)) {
            return WSAEAFNOSUPPORT;
        }
    }

    /* If this flag is set, we already made this listen call in xfer. */
    if (!(handle->flags & UV_HANDLE_SHARED_TCP_SOCKET) &&
        listen(handle->socket, backlog) == SOCKET_ERROR) {
        return WSAGetLastError();
    }

    handle->flags |= UV_HANDLE_LISTENING;
    handle->stream.serv.connection_cb = cb;
    INCREASE_ACTIVE_COUNT(loop, handle);

    simultaneous_accepts = handle->flags & UV_HANDLE_TCP_SINGLE_ACCEPT ? 1
        : uv_simultaneous_server_accepts;

    if (handle->tcp.serv.accept_reqs == NULL) {
        handle->tcp.serv.accept_reqs =
            uv__malloc(uv_simultaneous_server_accepts * sizeof(uv_tcp_accept_t));
        if (!handle->tcp.serv.accept_reqs) {
            uv_fatal_error(ERROR_OUTOFMEMORY, "uv__malloc");
        }

        for (i = 0; i < simultaneous_accepts; i++) {
            req = &handle->tcp.serv.accept_reqs[i];
            UV_REQ_INIT(req, UV_ACCEPT);
            req->accept_socket = INVALID_SOCKET;
            req->data = handle;

            req->wait_handle = INVALID_HANDLE_VALUE;
            if (handle->flags & UV_HANDLE_EMULATE_IOCP) {
                req->event_handle = CreateEvent(NULL, 0, 0, NULL);
                if (req->event_handle == NULL) {
                    uv_fatal_error(GetLastError(), "CreateEvent");
                }
            } else {
                req->event_handle = NULL;
            }

            uv_tcp_queue_accept(handle, req);
        }

        /* Initialize other unused requests too, because uv_tcp_endgame doesn't
         * know how many requests were initialized, so it will try to clean up
         * {uv_simultaneous_server_accepts} requests. */
        for (i = simultaneous_accepts; i < uv_simultaneous_server_accepts; i++) {
            req = &handle->tcp.serv.accept_reqs[i];
            UV_REQ_INIT(req, UV_ACCEPT);
            req->accept_socket = INVALID_SOCKET;
            req->data = handle;
            req->wait_handle = INVALID_HANDLE_VALUE;
            req->event_handle = NULL;
        }
    }

    return 0;
}


int uv_tcp_accept(uv_tcp_t* server, uv_tcp_t* client) {
    uv_loop_t* loop = server->loop;
    int err = 0;
    int family;

    uv_tcp_accept_t* req = server->tcp.serv.pending_accepts;

    if (!req) {
        /* No valid connections found, so we error out. */
        return WSAEWOULDBLOCK;
    }

    if (req->accept_socket == INVALID_SOCKET) {
        return WSAENOTCONN;
    }

    if (server->flags & UV_HANDLE_IPV6) {
        family = AF_INET6;
    } else {
        family = AF_INET;
    }

    err = uv_tcp_set_socket(client->loop,
                            client,
                            req->accept_socket,
                            family,
                            0);
    if (err) {
        closesocket(req->accept_socket);
    } else {
        uv_connection_init((uv_stream_t*)client);
        /* AcceptEx() implicitly binds the accepted socket. */
        client->flags |= UV_HANDLE_BOUND | UV_HANDLE_READABLE | UV_HANDLE_WRITABLE;
    }

    /* Prepare the req to pick up a new connection */
    server->tcp.serv.pending_accepts = req->next_pending;
    req->next_pending = NULL;
    req->accept_socket = INVALID_SOCKET;

    if (!(server->flags & UV_HANDLE_CLOSING)) {
        /* Check if we're in a middle of changing the number of pending accepts. */
        if (!(server->flags & UV_HANDLE_TCP_ACCEPT_STATE_CHANGING)) {
            uv_tcp_queue_accept(server, req);
        } else {
            /* We better be switching to a single pending accept. */
            assert(server->flags & UV_HANDLE_TCP_SINGLE_ACCEPT);

            server->tcp.serv.processed_accepts++;

            if (server->tcp.serv.processed_accepts >= uv_simultaneous_server_accepts) {
                server->tcp.serv.processed_accepts = 0;
                /*
                 * All previously queued accept requests are now processed.
                 * We now switch to queueing just a single accept.
                 */
                uv_tcp_queue_accept(server, &server->tcp.serv.accept_reqs[0]);
                server->flags &= ~UV_HANDLE_TCP_ACCEPT_STATE_CHANGING;
                server->flags |= UV_HANDLE_TCP_SINGLE_ACCEPT;
            }
        }
    }

    loop->active_tcp_streams++;

    return err;
}


int uv_tcp_read_start(uv_tcp_t* handle, uv_alloc_cb alloc_cb,
                      uv_read_cb read_cb) {
    uv_loop_t* loop = handle->loop;

    handle->flags |= UV_HANDLE_READING;
    handle->read_cb = read_cb;
    handle->alloc_cb = alloc_cb;
    INCREASE_ACTIVE_COUNT(loop, handle);

    /* If reading was stopped and then started again, there could still be a read
     * request pending. */
    if (!(handle->flags & UV_HANDLE_READ_PENDING)) {
        if (handle->flags & UV_HANDLE_EMULATE_IOCP &&
            handle->read_req.event_handle == NULL) {
            handle->read_req.event_handle = CreateEvent(NULL, 0, 0, NULL);
            if (handle->read_req.event_handle == NULL) {
                uv_fatal_error(GetLastError(), "CreateEvent");
            }
        }
        uv_tcp_queue_read(loop, handle);
    }

    return 0;
}

static int uv__is_loopback(const struct sockaddr_storage* storage) {
    const struct sockaddr_in* in4;
    const struct sockaddr_in6* in6;
    int i;

    if (storage->ss_family == AF_INET) {
        in4 = (const struct sockaddr_in*)storage;
        return in4->sin_addr.S_un.S_un_b.s_b1 == 127;
    }
    if (storage->ss_family == AF_INET6) {
        in6 = (const struct sockaddr_in6*)storage;
        for (i = 0; i < 7; ++i) {
            if (in6->sin6_addr.u.Word[i] != 0)
                return 0;
        }
        return in6->sin6_addr.u.Word[7] == htons(1);
    }
    return 0;
}

// Check if Windows version is 10.0.16299 or later
static int uv__is_fast_loopback_fail_supported(void) {
    OSVERSIONINFOW os_info;
    if (!pRtlGetVersion)
        return 0;
    pRtlGetVersion(&os_info);
    if (os_info.dwMajorVersion < 10)
        return 0;
    if (os_info.dwMajorVersion > 10)
        return 1;
    if (os_info.dwMinorVersion > 0)
        return 1;
    return os_info.dwBuildNumber >= 16299;
}

static int uv_tcp_try_connect(uv_connect_t* req,
                              uv_tcp_t* handle,
                              const struct sockaddr* addr,
                              unsigned int addrlen,
                              uv_connect_cb cb) {
    uv_loop_t* loop = handle->loop;
    TCP_INITIAL_RTO_PARAMETERS retransmit_ioctl;
    const struct sockaddr* bind_addr;
    struct sockaddr_storage converted;
    BOOL success;
    DWORD bytes;
    int err;

    err = uv__convert_to_localhost_if_unspecified(addr, &converted);
    if (err)
        return err;

    if (handle->delayed_error != 0)
        goto out;

    if (!(handle->flags & UV_HANDLE_BOUND)) {
        if (addrlen == sizeof(uv_addr_ip4_any_)) {
            bind_addr = (const struct sockaddr*)&uv_addr_ip4_any_;
        } else if (addrlen == sizeof(uv_addr_ip6_any_)) {
            bind_addr = (const struct sockaddr*)&uv_addr_ip6_any_;
        } else {
            abort();
        }
        err = uv_tcp_try_bind(handle, bind_addr, addrlen, 0);
        if (err)
            return err;
        if (handle->delayed_error != 0)
            goto out;
    }

    if (!handle->tcp.conn.func_connectex) {
        if (!uv_get_connectex_function(handle->socket, &handle->tcp.conn.func_connectex)) {
            return WSAEAFNOSUPPORT;
        }
    }

    /* This makes connect() fail instantly if the target port on the localhost
     * is not reachable, instead of waiting for 2s. We do not care if this fails.
     * This only works on Windows version 10.0.16299 and later.
     */
    if (uv__is_fast_loopback_fail_supported() && uv__is_loopback(&converted)) {
        memset(&retransmit_ioctl, 0, sizeof(retransmit_ioctl));
        retransmit_ioctl.Rtt = TCP_INITIAL_RTO_NO_SYN_RETRANSMISSIONS;
        retransmit_ioctl.MaxSynRetransmissions = TCP_INITIAL_RTO_NO_SYN_RETRANSMISSIONS;
        WSAIoctl(handle->socket,
                 SIO_TCP_INITIAL_RTO,
                 &retransmit_ioctl,
                 sizeof(retransmit_ioctl),
                 NULL,
                 0,
                 &bytes,
                 NULL,
                 NULL);
    }

out:

    UV_REQ_INIT(req, UV_CONNECT);
    req->handle = (uv_stream_t*)handle;
    req->cb = cb;
    memset(&req->u.io.overlapped, 0, sizeof(req->u.io.overlapped));

    if (handle->delayed_error != 0) {
        /* Process the req without IOCP. */
        handle->reqs_pending++;
        REGISTER_HANDLE_REQ(loop, handle, req);
        uv_insert_pending_req(loop, (uv_req_t*)req);
        return 0;
    }

    success = handle->tcp.conn.func_connectex(handle->socket,
                                              (const struct sockaddr*)&converted,
                                              addrlen,
                                              NULL,
                                              0,
                                              &bytes,
                                              &req->u.io.overlapped);

    if (UV_SUCCEEDED_WITHOUT_IOCP(success)) {
        /* Process the req without IOCP. */
        handle->reqs_pending++;
        REGISTER_HANDLE_REQ(loop, handle, req);
        uv_insert_pending_req(loop, (uv_req_t*)req);
    } else if (UV_SUCCEEDED_WITH_IOCP(success)) {
        /* The req will be processed with IOCP. */
        handle->reqs_pending++;
        REGISTER_HANDLE_REQ(loop, handle, req);
    } else {
        return WSAGetLastError();
    }

    return 0;
}


int uv_tcp_getsockname(const uv_tcp_t* handle,
                       struct sockaddr* name,
                       int* namelen) {

    return uv__getsockpeername((const uv_handle_t*)handle,
                               getsockname,
                               name,
                               namelen,
                               handle->delayed_error);
}


int uv_tcp_getpeername(const uv_tcp_t* handle,
                       struct sockaddr* name,
                       int* namelen) {

    return uv__getsockpeername((const uv_handle_t*)handle,
                               getpeername,
                               name,
                               namelen,
                               handle->delayed_error);
}


int uv_tcp_write(uv_loop_t* loop,
                 uv_write_t* req,
                 uv_tcp_t* handle,
                 const uv_buf_t bufs[],
                 unsigned int nbufs,
                 uv_write_cb cb) {
    int result;
    DWORD bytes;

    UV_REQ_INIT(req, UV_WRITE);
    req->handle = (uv_stream_t*)handle;
    req->cb = cb;

    /* Prepare the overlapped structure. */
    memset(&(req->u.io.overlapped), 0, sizeof(req->u.io.overlapped));
    if (handle->flags & UV_HANDLE_EMULATE_IOCP) {
        req->event_handle = CreateEvent(NULL, 0, 0, NULL);
        if (req->event_handle == NULL) {
            uv_fatal_error(GetLastError(), "CreateEvent");
        }
        req->u.io.overlapped.hEvent = (HANDLE)((ULONG_PTR)req->event_handle | 1);
        req->wait_handle = INVALID_HANDLE_VALUE;
    }

    result = WSASend(handle->socket,
                     (WSABUF*)bufs,
                     nbufs,
                     &bytes,
                     0,
                     &req->u.io.overlapped,
                     NULL);

    if (UV_SUCCEEDED_WITHOUT_IOCP(result == 0)) {
        /* Request completed immediately. */
        req->u.io.queued_bytes = 0;
        handle->reqs_pending++;
        handle->stream.conn.write_reqs_pending++;
        REGISTER_HANDLE_REQ(loop, handle, req);
        uv_insert_pending_req(loop, (uv_req_t*)req);
    } else if (UV_SUCCEEDED_WITH_IOCP(result == 0)) {
        /* Request queued by the kernel. */
        req->u.io.queued_bytes = uv__count_bufs(bufs, nbufs);
        handle->reqs_pending++;
        handle->stream.conn.write_reqs_pending++;
        REGISTER_HANDLE_REQ(loop, handle, req);
        handle->write_queue_size += req->u.io.queued_bytes;
        if (handle->flags & UV_HANDLE_EMULATE_IOCP &&
            !RegisterWaitForSingleObject(&req->wait_handle,
                                         req->event_handle, post_write_completion, (void*)req,
                                         INFINITE, WT_EXECUTEINWAITTHREAD | WT_EXECUTEONLYONCE)) {
            SET_REQ_ERROR(req, GetLastError());
            uv_insert_pending_req(loop, (uv_req_t*)req);
        }
    } else {
        /* Send failed due to an error, report it later */
        req->u.io.queued_bytes = 0;
        handle->reqs_pending++;
        handle->stream.conn.write_reqs_pending++;
        REGISTER_HANDLE_REQ(loop, handle, req);
        SET_REQ_ERROR(req, WSAGetLastError());
        uv_insert_pending_req(loop, (uv_req_t*)req);
    }

    return 0;
}


int uv__tcp_try_write(uv_tcp_t* handle,
                      const uv_buf_t bufs[],
                      unsigned int nbufs) {
    int result;
    DWORD bytes;

    if (handle->stream.conn.write_reqs_pending > 0)
        return UV_EAGAIN;

    result = WSASend(handle->socket,
                     (WSABUF*)bufs,
                     nbufs,
                     &bytes,
                     0,
                     NULL,
                     NULL);

    if (result == SOCKET_ERROR)
        return uv_translate_sys_error(WSAGetLastError());
    else
        return bytes;
}


void uv_process_tcp_read_req(uv_loop_t* loop, uv_tcp_t* handle,
                             uv_req_t* req) {
    DWORD bytes, flags, err;
    uv_buf_t buf;
    int count;

    assert(handle->type == UV_TCP);

    handle->flags &= ~UV_HANDLE_READ_PENDING;

    if (!REQ_SUCCESS(req)) {
        /* An error occurred doing the read. */
        if ((handle->flags & UV_HANDLE_READING) ||
            !(handle->flags & UV_HANDLE_ZERO_READ)) {
            handle->flags &= ~UV_HANDLE_READING;
            DECREASE_ACTIVE_COUNT(loop, handle);
            buf = (handle->flags & UV_HANDLE_ZERO_READ) ?
                uv_buf_init(NULL, 0) : handle->tcp.conn.read_buffer;

            err = GET_REQ_SOCK_ERROR(req);

            if (err == WSAECONNABORTED) {
                /* Turn WSAECONNABORTED into UV_ECONNRESET to be consistent with Unix.
                 */
                err = WSAECONNRESET;
            }
            handle->flags &= ~(UV_HANDLE_READABLE | UV_HANDLE_WRITABLE);

            handle->read_cb((uv_stream_t*)handle,
                            uv_translate_sys_error(err),
                            &buf);
        }
    } else {
        if (!(handle->flags & UV_HANDLE_ZERO_READ)) {
            /* The read was done with a non-zero buffer length. */
            if (req->u.io.overlapped.InternalHigh > 0) {
                /* Successful read */
                handle->read_cb((uv_stream_t*)handle,
                                req->u.io.overlapped.InternalHigh,
                                &handle->tcp.conn.read_buffer);
                /* Read again only if bytes == buf.len */
                if (req->u.io.overlapped.InternalHigh < handle->tcp.conn.read_buffer.len) {
                    goto done;
                }
            } else {
                /* Connection closed */
                if (handle->flags & UV_HANDLE_READING) {
                    handle->flags &= ~UV_HANDLE_READING;
                    DECREASE_ACTIVE_COUNT(loop, handle);
                }

                buf.base = 0;
                buf.len = 0;
                handle->read_cb((uv_stream_t*)handle, UV_EOF, &handle->tcp.conn.read_buffer);
                goto done;
            }
        }

        /* Do nonblocking reads until the buffer is empty */
        count = 32;
        while ((handle->flags & UV_HANDLE_READING) && (count-- > 0)) {
            buf = uv_buf_init(NULL, 0);
            handle->alloc_cb((uv_handle_t*)handle, 65536, &buf);
            if (buf.base == NULL || buf.len == 0) {
                handle->read_cb((uv_stream_t*)handle, UV_ENOBUFS, &buf);
                break;
            }
            assert(buf.base != NULL);

            flags = 0;
            if (WSARecv(handle->socket,
                        (WSABUF*)&buf,
                        1,
                        &bytes,
                        &flags,
                        NULL,
                        NULL) != SOCKET_ERROR) {
                if (bytes > 0) {
                    /* Successful read */
                    handle->read_cb((uv_stream_t*)handle, bytes, &buf);
                    /* Read again only if bytes == buf.len */
                    if (bytes < buf.len) {
                        break;
                    }
                } else {
                    /* Connection closed */
                    handle->flags &= ~UV_HANDLE_READING;
                    DECREASE_ACTIVE_COUNT(loop, handle);

                    handle->read_cb((uv_stream_t*)handle, UV_EOF, &buf);
                    break;
                }
            } else {
                err = WSAGetLastError();
                if (err == WSAEWOULDBLOCK) {
                    /* Read buffer was completely empty, report a 0-byte read. */
                    handle->read_cb((uv_stream_t*)handle, 0, &buf);
                } else {
                    /* Ouch! serious error. */
                    handle->flags &= ~UV_HANDLE_READING;
                    DECREASE_ACTIVE_COUNT(loop, handle);

                    if (err == WSAECONNABORTED) {
                        /* Turn WSAECONNABORTED into UV_ECONNRESET to be consistent with
                         * Unix. */
                        err = WSAECONNRESET;
                    }
                    handle->flags &= ~(UV_HANDLE_READABLE | UV_HANDLE_WRITABLE);

                    handle->read_cb((uv_stream_t*)handle,
                                    uv_translate_sys_error(err),
                                    &buf);
                }
                break;
            }
        }

    done:
        /* Post another read if still reading and not closing. */
        if ((handle->flags & UV_HANDLE_READING) &&
            !(handle->flags & UV_HANDLE_READ_PENDING)) {
            uv_tcp_queue_read(loop, handle);
        }
    }

    DECREASE_PENDING_REQ_COUNT(handle);
}


void uv_process_tcp_write_req(uv_loop_t* loop, uv_tcp_t* handle,
                              uv_write_t* req) {
    int err;

    assert(handle->type == UV_TCP);

    assert(handle->write_queue_size >= req->u.io.queued_bytes);
    handle->write_queue_size -= req->u.io.queued_bytes;

    UNREGISTER_HANDLE_REQ(loop, handle, req);

    if (handle->flags & UV_HANDLE_EMULATE_IOCP) {
        if (req->wait_handle != INVALID_HANDLE_VALUE) {
            UnregisterWait(req->wait_handle);
            req->wait_handle = INVALID_HANDLE_VALUE;
        }
        if (req->event_handle != NULL) {
            CloseHandle(req->event_handle);
            req->event_handle = NULL;
        }
    }

    if (req->cb) {
        err = uv_translate_sys_error(GET_REQ_SOCK_ERROR(req));
        if (err == UV_ECONNABORTED) {
            /* use UV_ECANCELED for consistency with Unix */
            err = UV_ECANCELED;
        }
        req->cb(req, err);
    }

    handle->stream.conn.write_reqs_pending--;
    if (handle->stream.conn.write_reqs_pending == 0) {
        if (handle->flags & UV_HANDLE_CLOSING) {
            closesocket(handle->socket);
            handle->socket = INVALID_SOCKET;
        }
        if (handle->stream.conn.shutdown_req != NULL) {
            uv_want_endgame(loop, (uv_handle_t*)handle);
        }
    }

    DECREASE_PENDING_REQ_COUNT(handle);
}


void uv_process_tcp_accept_req(uv_loop_t* loop, uv_tcp_t* handle,
                               uv_req_t* raw_req) {
    uv_tcp_accept_t* req = (uv_tcp_accept_t*)raw_req;
    int err;

    assert(handle->type == UV_TCP);

    /* If handle->accepted_socket is not a valid socket, then uv_queue_accept
     * must have failed. This is a serious error. We stop accepting connections
     * and report this error to the connection callback. */
    if (req->accept_socket == INVALID_SOCKET) {
        if (handle->flags & UV_HANDLE_LISTENING) {
            handle->flags &= ~UV_HANDLE_LISTENING;
            DECREASE_ACTIVE_COUNT(loop, handle);
            if (handle->stream.serv.connection_cb) {
                err = GET_REQ_SOCK_ERROR(req);
                handle->stream.serv.connection_cb((uv_stream_t*)handle,
                                                  uv_translate_sys_error(err));
            }
        }
    } else if (REQ_SUCCESS(req) &&
               setsockopt(req->accept_socket,
                          SOL_SOCKET,
                          SO_UPDATE_ACCEPT_CONTEXT,
                          (char*)&handle->socket,
                          sizeof(handle->socket)) == 0) {
        req->next_pending = handle->tcp.serv.pending_accepts;
        handle->tcp.serv.pending_accepts = req;

        /* Accept and SO_UPDATE_ACCEPT_CONTEXT were successful. */
        if (handle->stream.serv.connection_cb) {
            handle->stream.serv.connection_cb((uv_stream_t*)handle, 0);
        }
    } else {
        /* Error related to accepted socket is ignored because the server socket
         * may still be healthy. If the server socket is broken uv_queue_accept
         * will detect it. */
        closesocket(req->accept_socket);
        req->accept_socket = INVALID_SOCKET;
        if (handle->flags & UV_HANDLE_LISTENING) {
            uv_tcp_queue_accept(handle, req);
        }
    }

    DECREASE_PENDING_REQ_COUNT(handle);
}


void uv_process_tcp_connect_req(uv_loop_t* loop, uv_tcp_t* handle,
                                uv_connect_t* req) {
    int err;

    assert(handle->type == UV_TCP);

    UNREGISTER_HANDLE_REQ(loop, handle, req);

    err = 0;
    if (handle->delayed_error) {
        /* To smooth over the differences between unixes errors that
         * were reported synchronously on the first connect can be delayed
         * until the next tick--which is now.
         */
        err = handle->delayed_error;
        handle->delayed_error = 0;
    } else if (REQ_SUCCESS(req)) {
        if (handle->flags & UV_HANDLE_CLOSING) {
            /* use UV_ECANCELED for consistency with Unix */
            err = ERROR_OPERATION_ABORTED;
        } else if (setsockopt(handle->socket,
                              SOL_SOCKET,
                              SO_UPDATE_CONNECT_CONTEXT,
                              NULL,
                              0) == 0) {
            uv_connection_init((uv_stream_t*)handle);
            handle->flags |= UV_HANDLE_READABLE | UV_HANDLE_WRITABLE;
            loop->active_tcp_streams++;
        } else {
            err = WSAGetLastError();
        }
    } else {
        err = GET_REQ_SOCK_ERROR(req);
    }
    req->cb(req, uv_translate_sys_error(err));

    DECREASE_PENDING_REQ_COUNT(handle);
}


int uv__tcp_xfer_export(uv_tcp_t* handle,
                        int target_pid,
                        uv__ipc_socket_xfer_type_t* xfer_type,
                        uv__ipc_socket_xfer_info_t* xfer_info) {
    if (handle->flags & UV_HANDLE_CONNECTION) {
        *xfer_type = UV__IPC_SOCKET_XFER_TCP_CONNECTION;
    } else {
        *xfer_type = UV__IPC_SOCKET_XFER_TCP_SERVER;
        /* We're about to share the socket with another process. Because this is a
         * listening socket, we assume that the other process will be accepting
         * connections on it. Thus, before sharing the socket with another process,
         * we call listen here in the parent process. */
        if (!(handle->flags & UV_HANDLE_LISTENING)) {
            if (!(handle->flags & UV_HANDLE_BOUND)) {
                return ERROR_NOT_SUPPORTED;
            }
            if (handle->delayed_error == 0 &&
                listen(handle->socket, SOMAXCONN) == SOCKET_ERROR) {
                handle->delayed_error = WSAGetLastError();
            }
        }
    }

    if (WSADuplicateSocketW(handle->socket, target_pid, &xfer_info->socket_info))
        return WSAGetLastError();
    xfer_info->delayed_error = handle->delayed_error;

    /* Mark the local copy of the handle as 'shared' so we behave in a way that's
     * friendly to the process(es) that we share the socket with. */
    handle->flags |= UV_HANDLE_SHARED_TCP_SOCKET;

    return 0;
}


int uv__tcp_xfer_import(uv_tcp_t* tcp,
                        uv__ipc_socket_xfer_type_t xfer_type,
                        uv__ipc_socket_xfer_info_t* xfer_info) {
    int err;
    SOCKET socket;

    assert(xfer_type == UV__IPC_SOCKET_XFER_TCP_SERVER ||
           xfer_type == UV__IPC_SOCKET_XFER_TCP_CONNECTION);

    socket = WSASocketW(FROM_PROTOCOL_INFO,
                        FROM_PROTOCOL_INFO,
                        FROM_PROTOCOL_INFO,
                        &xfer_info->socket_info,
                        0,
                        WSA_FLAG_OVERLAPPED);

    if (socket == INVALID_SOCKET) {
        return WSAGetLastError();
    }

    err = uv_tcp_set_socket(
        tcp->loop, tcp, socket, xfer_info->socket_info.iAddressFamily, 1);
    if (err) {
        closesocket(socket);
        return err;
    }

    tcp->delayed_error = xfer_info->delayed_error;
    tcp->flags |= UV_HANDLE_BOUND | UV_HANDLE_SHARED_TCP_SOCKET;

    if (xfer_type == UV__IPC_SOCKET_XFER_TCP_CONNECTION) {
        uv_connection_init((uv_stream_t*)tcp);
        tcp->flags |= UV_HANDLE_READABLE | UV_HANDLE_WRITABLE;
    }

    tcp->loop->active_tcp_streams++;
    return 0;
}


int uv_tcp_nodelay(uv_tcp_t* handle, int enable) {
    int err;

    if (handle->socket != INVALID_SOCKET) {
        err = uv__tcp_nodelay(handle, handle->socket, enable);
        if (err)
            return uv_translate_sys_error(err);
    }

    if (enable) {
        handle->flags |= UV_HANDLE_TCP_NODELAY;
    } else {
        handle->flags &= ~UV_HANDLE_TCP_NODELAY;
    }

    return 0;
}


int uv_tcp_keepalive(uv_tcp_t* handle, int enable, unsigned int delay) {
    int err;

    if (handle->socket != INVALID_SOCKET) {
        err = uv__tcp_keepalive(handle, handle->socket, enable, delay);
        if (err)
            return uv_translate_sys_error(err);
    }

    if (enable) {
        handle->flags |= UV_HANDLE_TCP_KEEPALIVE;
    } else {
        handle->flags &= ~UV_HANDLE_TCP_KEEPALIVE;
    }

    /* TODO: Store delay if handle->socket isn't created yet. */

    return 0;
}


int uv_tcp_simultaneous_accepts(uv_tcp_t* handle, int enable) {
    if (handle->flags & UV_HANDLE_CONNECTION) {
        return UV_EINVAL;
    }

    /* Check if we're already in the desired mode. */
    if ((enable && !(handle->flags & UV_HANDLE_TCP_SINGLE_ACCEPT)) ||
        (!enable && handle->flags & UV_HANDLE_TCP_SINGLE_ACCEPT)) {
        return 0;
    }

    /* Don't allow switching from single pending accept to many. */
    if (enable) {
        return UV_ENOTSUP;
    }

    /* Check if we're in a middle of changing the number of pending accepts. */
    if (handle->flags & UV_HANDLE_TCP_ACCEPT_STATE_CHANGING) {
        return 0;
    }

    handle->flags |= UV_HANDLE_TCP_SINGLE_ACCEPT;

    /* Flip the changing flag if we have already queued multiple accepts. */
    if (handle->flags & UV_HANDLE_LISTENING) {
        handle->flags |= UV_HANDLE_TCP_ACCEPT_STATE_CHANGING;
    }

    return 0;
}


static void uv_tcp_try_cancel_reqs(uv_tcp_t* tcp) {
    SOCKET socket;
    int non_ifs_lsp;
    int reading;
    int writing;

    socket = tcp->socket;
    reading = tcp->flags & UV_HANDLE_READING;
    writing = tcp->stream.conn.write_reqs_pending > 0;
    if (!reading && !writing)
        return;

    /* TODO: in libuv v2, keep explicit track of write_reqs, so we can cancel
     * them each explicitly with CancelIoEx (like unix). */
    if (reading)
        CancelIoEx((HANDLE)socket, &tcp->read_req.u.io.overlapped);
    if (writing)
        CancelIo((HANDLE)socket);

    /* Check if we have any non-IFS LSPs stacked on top of TCP */
    non_ifs_lsp = (tcp->flags & UV_HANDLE_IPV6) ? uv_tcp_non_ifs_lsp_ipv6 :
        uv_tcp_non_ifs_lsp_ipv4;

    /* If there are non-ifs LSPs then try to obtain a base handle for the socket.
     * This will always fail on Windows XP/3k. */
    if (non_ifs_lsp) {
        DWORD bytes;
        if (WSAIoctl(socket,
                     SIO_BASE_HANDLE,
                     NULL,
                     0,
                     &socket,
                     sizeof socket,
                     &bytes,
                     NULL,
                     NULL) != 0) {
            /* Failed. We can't do CancelIo. */
            return;
        }
    }

    assert(socket != 0 && socket != INVALID_SOCKET);

    if (socket != tcp->socket) {
        if (reading)
            CancelIoEx((HANDLE)socket, &tcp->read_req.u.io.overlapped);
        if (writing)
            CancelIo((HANDLE)socket);
    }
}


void uv_tcp_close(uv_loop_t* loop, uv_tcp_t* tcp) {
    if (tcp->flags & UV_HANDLE_CONNECTION) {
        uv_tcp_try_cancel_reqs(tcp);
        if (tcp->flags & UV_HANDLE_READING) {
            uv_read_stop((uv_stream_t*)tcp);
        }
    } else {
        if (tcp->tcp.serv.accept_reqs != NULL) {
            /* First close the incoming sockets to cancel the accept operations before
             * we free their resources. */
            unsigned int i;
            for (i = 0; i < uv_simultaneous_server_accepts; i++) {
                uv_tcp_accept_t* req = &tcp->tcp.serv.accept_reqs[i];
                if (req->accept_socket != INVALID_SOCKET) {
                    closesocket(req->accept_socket);
                    req->accept_socket = INVALID_SOCKET;
                }
            }
        }
        assert(!(tcp->flags & UV_HANDLE_READING));
    }

    if (tcp->flags & UV_HANDLE_LISTENING) {
        tcp->flags &= ~UV_HANDLE_LISTENING;
        DECREASE_ACTIVE_COUNT(loop, tcp);
    }

    /* If any overlapped req failed to cancel, calling `closesocket` now would
     * cause Win32 to send an RST packet. Try to avoid that for writes, if
     * possibly applicable, by waiting to process the completion notifications
     * first (which typically should be cancellations). There's not much we can
     * do about canceled reads, which also will generate an RST packet. */
    if (!(tcp->flags & UV_HANDLE_CONNECTION) ||
        tcp->stream.conn.write_reqs_pending == 0) {
        closesocket(tcp->socket);
        tcp->socket = INVALID_SOCKET;
    }

    tcp->flags &= ~(UV_HANDLE_READABLE | UV_HANDLE_WRITABLE);
    uv__handle_closing(tcp);

    if (tcp->reqs_pending == 0) {
        uv_want_endgame(tcp->loop, (uv_handle_t*)tcp);
    }
}


int uv_tcp_open(uv_tcp_t* handle, uv_os_sock_t sock) {
    WSAPROTOCOL_INFOW protocol_info;
    int opt_len;
    int err;
    struct sockaddr_storage saddr;
    int saddr_len;

    /* Detect the address family of the socket. */
    opt_len = (int)sizeof protocol_info;
    if (getsockopt(sock,
                   SOL_SOCKET,
                   SO_PROTOCOL_INFOW,
                   (char*)&protocol_info,
                   &opt_len) == SOCKET_ERROR) {
        return uv_translate_sys_error(GetLastError());
    }

    err = uv_tcp_set_socket(handle->loop,
                            handle,
                            sock,
                            protocol_info.iAddressFamily,
                            1);
    if (err) {
        return uv_translate_sys_error(err);
    }

    /* Support already active socket. */
    saddr_len = sizeof(saddr);
    if (!uv_tcp_getsockname(handle, (struct sockaddr*)&saddr, &saddr_len)) {
        /* Socket is already bound. */
        handle->flags |= UV_HANDLE_BOUND;
        saddr_len = sizeof(saddr);
        if (!uv_tcp_getpeername(handle, (struct sockaddr*)&saddr, &saddr_len)) {
            /* Socket is already connected. */
            uv_connection_init((uv_stream_t*)handle);
            handle->flags |= UV_HANDLE_READABLE | UV_HANDLE_WRITABLE;
        }
    }

    return 0;
}


/* This function is an egress point, i.e. it returns libuv errors rather than
 * system errors.
 */
int uv__tcp_bind(uv_tcp_t* handle,
                 const struct sockaddr* addr,
                 unsigned int addrlen,
                 unsigned int flags) {
    int err;

    err = uv_tcp_try_bind(handle, addr, addrlen, flags);
    if (err)
        return uv_translate_sys_error(err);

    return 0;
}


/* This function is an egress point, i.e. it returns libuv errors rather than
 * system errors.
 */
int uv__tcp_connect(uv_connect_t* req,
                    uv_tcp_t* handle,
                    const struct sockaddr* addr,
                    unsigned int addrlen,
                    uv_connect_cb cb) {
    int err;

    err = uv_tcp_try_connect(req, handle, addr, addrlen, cb);
    if (err)
        return uv_translate_sys_error(err);

    return 0;
}

#ifndef WSA_FLAG_NO_HANDLE_INHERIT
/* Added in Windows 7 SP1. Specify this to avoid race conditions, */
/* but also manually clear the inherit flag in case this failed. */
#define WSA_FLAG_NO_HANDLE_INHERIT 0x80
#endif

int uv_socketpair(int type, int protocol, uv_os_sock_t fds[2], int flags0, int flags1) {
    SOCKET server = INVALID_SOCKET;
    SOCKET client0 = INVALID_SOCKET;
    SOCKET client1 = INVALID_SOCKET;
    SOCKADDR_IN name;
    LPFN_ACCEPTEX func_acceptex;
    WSAOVERLAPPED overlap;
    char accept_buffer[sizeof(struct sockaddr_storage) * 2 + 32];
    int namelen;
    int err;
    DWORD bytes;
    DWORD flags;
    DWORD client0_flags = WSA_FLAG_NO_HANDLE_INHERIT;
    DWORD client1_flags = WSA_FLAG_NO_HANDLE_INHERIT;

    if (flags0 & UV_NONBLOCK_PIPE)
        client0_flags |= WSA_FLAG_OVERLAPPED;
    if (flags1 & UV_NONBLOCK_PIPE)
        client1_flags |= WSA_FLAG_OVERLAPPED;

    server = WSASocketW(AF_INET, type, protocol, NULL, 0,
                        WSA_FLAG_OVERLAPPED | WSA_FLAG_NO_HANDLE_INHERIT);
    if (server == INVALID_SOCKET)
        goto wsaerror;
    if (!SetHandleInformation((HANDLE)server, HANDLE_FLAG_INHERIT, 0))
        goto error;
    name.sin_family = AF_INET;
    name.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
    name.sin_port = 0;
    if (bind(server, (SOCKADDR*)&name, sizeof(name)) != 0)
        goto wsaerror;
    if (listen(server, 1) != 0)
        goto wsaerror;
    namelen = sizeof(name);
    if (getsockname(server, (SOCKADDR*)&name, &namelen) != 0)
        goto wsaerror;
    client0 = WSASocketW(AF_INET, type, protocol, NULL, 0, client0_flags);
    if (client0 == INVALID_SOCKET)
        goto wsaerror;
    if (!SetHandleInformation((HANDLE)client0, HANDLE_FLAG_INHERIT, 0))
        goto error;
    if (connect(client0, (SOCKADDR*)&name, sizeof(name)) != 0)
        goto wsaerror;
    client1 = WSASocketW(AF_INET, type, protocol, NULL, 0, client1_flags);
    if (client1 == INVALID_SOCKET)
        goto wsaerror;
    if (!SetHandleInformation((HANDLE)client1, HANDLE_FLAG_INHERIT, 0))
        goto error;
    if (!uv_get_acceptex_function(server, &func_acceptex)) {
        err = WSAEAFNOSUPPORT;
        goto cleanup;
    }
    memset(&overlap, 0, sizeof(overlap));
    if (!func_acceptex(server,
                       client1,
                       accept_buffer,
                       0,
                       sizeof(struct sockaddr_storage),
                       sizeof(struct sockaddr_storage),
                       &bytes,
                       &overlap)) {
        err = WSAGetLastError();
        if (err == ERROR_IO_PENDING) {
            /* Result should complete immediately, since we already called connect,
             * but empirically, we sometimes have to poll the kernel a couple times
             * until it notices that. */
            while (!WSAGetOverlappedResult(client1, &overlap, &bytes, FALSE, &flags)) {
                err = WSAGetLastError();
                if (err != WSA_IO_INCOMPLETE)
                    goto cleanup;
                SwitchToThread();
            }
        } else {
            goto cleanup;
        }
    }
    if (setsockopt(client1, SOL_SOCKET, SO_UPDATE_ACCEPT_CONTEXT,
                   (char*)&server, sizeof(server)) != 0) {
        goto wsaerror;
    }

    closesocket(server);

    fds[0] = client0;
    fds[1] = client1;

    return 0;

wsaerror:
    err = WSAGetLastError();
    goto cleanup;

error:
    err = GetLastError();
    goto cleanup;

cleanup:
    if (server != INVALID_SOCKET)
        closesocket(server);
    if (client0 != INVALID_SOCKET)
        closesocket(client0);
    if (client1 != INVALID_SOCKET)
        closesocket(client1);

    assert(err);
    return uv_translate_sys_error(err);
}
